Astrocytes are a widespread group of cells in the human brain, as well as in the brains of other mammals, and are the largest of all glial cells. Their main function is to separate and support neuronal cells. Astrocytes have many protrusions that stretch out to fill the neuronal cells and the gaps between the protrusions to support them, keep them structurally stable and separate them so that the impulses between the neuronal cells and their synapses are not disrupted. Astrocytes are also involved in the formation of the blood-brain barrier, which is a very important tissue for the brain. It separates the blood from the brain and prevents harmful substances in the blood from entering the brain through it.